This invention relates generally to integrated circuits, and more particularly to Micro Electro-Mechanical System (MEMS) switches.
Rapid advances in the field of telecommunications have been paced by improvements in the electronic devices and systems which make the transfer of information possible. Switches that allow the routing of electronic signals are important components in any communication system. Switches that perform well at high frequencies are particularly valuable. Although the p-i-n diode is a popular RF switch, it has problems with high power consumption because the diode must be forward biased to provide carriers for the low impedance state. Furthermore, the p-i-n diode suffers from high cost and nonlinearity.
Recently, (MEMS) switches have been developed for switching RF signals. FIG. 1 shows a cross-sectional view of an RF drumhead capacitive MEMS switch 10, disclosed by Goldsmith et al. in U.S. Pat. No. 5,619,061. An insulator 14 such as SiO2 is deposited over a substrate 12 such as silicon. A bottom electrode 16 is formed on insulator 14 and a dielectric 18 is formed over bottom electrode 16. Capacitor dielectric 18 typically comprises Si3N4, Ta2O5 or other suitable dielectric materials, for example. An active element comprising a thin metallic membrane 22 is suspended away from electrode 16 by insulating spacers 20. Membrane 22 is movable through the application of a DC electrostatic field across membrane 22, which serves as a top electrode, and bottom electrode 16. Membrane 22, dielectric 18 and bottom electrode 16 comprise a metal-dielectric-metal capacitor when the MEMS switch 10 is in the xe2x80x9conxe2x80x9d position. MEMS switches 10 have low insertion loss, good isolation, high power handling, and very low switching and static power requirements.
The present invention achieves technical advantages as a MEMS switch having a protective cap formed on the bottom electrode to prevent oxidation of the bottom electrode material, improving the capacitive effects of the MEMS switch. The protective cap comprises a material having a higher resistance to oxidation than the bottom electrode material or a material having an associated oxide, which oxide is a high dielectric contant (k) dielectric material (e.g. at least 20).
Disclosed is a MEMS switch, including a bottom electrode formed over a substrate, and a thin protective cap layer disposed over the bottom electrode. A dielectric material is disposed over the protective cap layer, and a spacer is placed proximate the bottom electrode. A pull-down electrode is disposed over the spacer and the dielectric material. The protective cap layer prevents the oxidation of the bottom electrode.
Also disclosed is a method of manufacturing a MEMS switch, comprising the steps of providing a substrate, depositing an insulator layer on the substrate, and forming a bottom electrode on the insulator layer. A thin protective cap layer is deposited over the bottom electrode, and a dielectric material is deposited over the bottom electrode and thin protective cap layer. A pull-down electrode is formed over the dielectric material. The thin protective cap layer prevents the oxidation of the bottom electrode.
Advantages of the invention include maintaining the capacitance of the dielectric stack of a MEMS switch. The protective cap layer comprises a material having a higher resistance to oxidation than the bottom electrode or a material that forms a high dielectric constant oxide upon oxidation, maintaining or improving the capacitance to the dielectric stack. The protective cap layer is easily implemented and only requires one more processing step.